This project will continue the development of high gradient magnetic cell sorting techniques with an emphasis on murine lymphocyte subpopulations which specifically bind antigen. The goals of the project will be twofold. The first will be to apply the magnetic rosette enrichment technique that has already been developed to the study of antigen-binding cells (ABC). The second will be to modify the magnetic methods so that (1) the rosette purifications can be carried out using an ordinary electromagnet and (2) ferritin labelled cells can be enriched using the high field superconducting magnet. The method in the study of ABC will be to physically fractionate mouse spleen or lymph node cells according to ability to bind antigen and then assay for evidence or proliferative response (increased nuclear DNA) or secretory response (hemolytic plaque formation). In this way the presence or absence of receptors for antigen can be correlated with the resting, proliferating and antibody-secreting stages of clonal maturation. A variation in the rosetting of ABC will make possible cell fractionations on the basis of functional affinity for antigen. This avidity will then be correlated with the frequency of triggerable precursors of antibody secreting cells using an adoptive transfer splenic fragment culture procedure. The adaptation of the rosette enrichment technique to a conventional laboratory electromagnet will make this versatile procedure more accessible to other laboratories as well as freeing the high field magnet for studies on the enrichment of ferritin labelled cells. The use of ferritin is the ultimate goal for the development of high gradient magnetic separation and the efficiency that can be achieved will depend on results from experiments to maximize the amount of paramagnetic ferritin per labelled cell and to minimize nonmagnetic trapping of unlabelled cells by the matrix in the column.